SiN is a common material used in semiconductor processes and devices, such as in patterning technology and flash memory. The challenge of using SiN is etching selectivity and etch rate. In the semiconductor processes, SiN usually needs to be etched from other silicon materials surrounding the SiN, for instance, SiO2. In 3D NAND device applications, after creating a high-aspect-ratio (HAR) aperture in a stacked structure of alternating SiN and SiO2 layers (ONON), SiN layers need to be removed inside the HAR aperture. Thus, horizontal isotropic etching of SiN with high selectivity to SiO2 and same etching rate of SiN at both top and bottom in the HAR aperture are required in 3D NAND device applications.
Wet etching process with H3PO4 may currently have been used to remove SiN in industry. However, when the HAR trench becomes deeper, there may be issues for liquid chemicals reaching to the bottom of the HAR trench due to surface tension effect. Dry etching therefore becomes a solution to develop. Dry etching may reduce process time and has less impurity introduction.
Typical dry etching process utilizes a plasma that produces anisotropic etch. Since horizontal etching of SiN requires isotropic etching, there is a need for isotropic etch process for which plasma may not be suited.
Various dry etching methods have been developed to perform isotropic etching SiN from SiO2. In addition, nitrosyl fluoride (FNO) has been used for etching SiN or silicon containing materials. For example, JP 4739709 to Tamaoki et al. discloses non-plasma cleaning or etching capability to SiN, SiC, and quartz with F2+NO chemistry and showed example that the selectivity of SiN/quartz to be 16. U.S. Pat. Nos. 5,376,234 and 5,445,712 to Yanagida discloses thermal etching of SiN and SiO2 with FNO chemistry, but no selectivity measures for other materials. U.S. Pat. Nos. 9,683,288 and 8,679,259 to Kameda et al. disclose a dry cleaning process in which FNO is generated by using a gas containing fluorine atoms with NO gas and supplied into a processing vessel. Kastenmeier et al. (J. Vac. Sci. Technol. A, 19 (2001) 25) discloses SiN etching in F2 and NO containing plasmas, but no selectivity measures for other materials. Yonemura et al. (J. Electrochem. Soc., 150 (2003) G707) reported the evaluation of SiO2 etching in FNO and F3NO containing gases, but no selectivity measures for other materials. Kigoshi et al. (Journal of the Mining and Metallurgical Institute of Japan, 89 (1973) p. 799) and Tajima et al. (J. Phys. Chem. C, 117 (2013) p. 20810) reported non-plasma etching to Si material using F2, NO, and FNO gases.
Other exemplary examples of etching Si, SiN or other silicon containing films include U.S. Pat. Nos. 3,882,040, 4,536,252, 6,380,095, US20010020516, US20080236482, US20080236483, US20100132744 and US20030143846.
As such, there is a need for developing isotropic etching methods to prove differentiation for specific etching gases that are suitable for use in specific etching processes with good selectivity properties.